This may seem silly, but for the life of me I can't seem to get my head around how a full-wave bridge using tubes.......well, works. It's the heater tying into the circuit.
Yeah I'm all over SS FWB but using tubes...I can't seem to get the electron flow down, I am confused with the heater & how it ties in.
The 5U4GB has the common Cathode with the twin Anodes.....so one just needs a pair right?
Does someone have a simple schematic including the heater set-up....like, do I need twin heater windings or can I use one winding for both, why or why not???
__________________________________________________Rick......
Yeah I'm all over SS FWB but using tubes...I can't seem to get the electron flow down, I am confused with the heater & how it ties in.
The 5U4GB has the common Cathode with the twin Anodes.....so one just needs a pair right?
Does someone have a simple schematic including the heater set-up....like, do I need twin heater windings or can I use one winding for both, why or why not???
__________________________________________________Rick......
Have a read of this item. It may enlighten you. The Valve Wizard Hope that explains the correct terminology.
It's likely the reason you don't see a lot of hollow-state FWB implementations, although there are some around that use other tubes with indirectly heated cathodes (no connection between cathode and heater) to get around the heater-supply problem.
The 5U4 and its variants are not suitable for FWB, IMO. The heater is the cathode, and the cathode is common in the tube. There are probably other reasons not to use it in this application, but the basic tube configuration is a show stopper.
You could, though, make a hybrid FWB - two SS rectifiers for the ground-leg and the 5U4 (or similar) for the positive leg. Several folks on this site have done this in their projects. The hybrid approach avoids using multiple rectifier tubes (each with significant voltage drop) to implement a tube FWB.
Good luck. 😎
Sam
The 5U4 and its variants are not suitable for FWB, IMO. The heater is the cathode, and the cathode is common in the tube. There are probably other reasons not to use it in this application, but the basic tube configuration is a show stopper.
You could, though, make a hybrid FWB - two SS rectifiers for the ground-leg and the 5U4 (or similar) for the positive leg. Several folks on this site have done this in their projects. The hybrid approach avoids using multiple rectifier tubes (each with significant voltage drop) to implement a tube FWB.
Good luck. 😎
Sam
Hi Jazbo8 - I think the OP was referring to a Full Wave Bridge. The circuit you show is a Full Wave with the plates paralleled, presumably to increase the current-carrying capacity of the circuit.
The FWB would not have a center-tapped transformer.
Sam
The FWB would not have a center-tapped transformer.
Sam
You are right, I have removed the link to avoid confusion. I always use the hybrid version myself, it's easier to deal with.
Hi!
For a FWB with 5U4, you'd need at least 3 tubes and 3 separate heater windings.
One tube would be connected to the secondary in the regular way, the plates connected to either end of the secondary and the raw rectified voltage drawn from the filament (cathode).
The two others would need to have the plates tied together. The paralleled plates of both would be the ground output of the rectifier bridge. The filaments would need to be connected to either end of the secondary.
As has been mentioned, much easier with indirectly heated tubes like 6AX4:
VinylSavor: Tube of the Month: The 6AX4
For higher voltages, exceeding about 900VDC a bridge with 6AX4 would also need separate heater windings. In the link above there is a schematic of such a bridge
Best regards
Thomas
For a FWB with 5U4, you'd need at least 3 tubes and 3 separate heater windings.
One tube would be connected to the secondary in the regular way, the plates connected to either end of the secondary and the raw rectified voltage drawn from the filament (cathode).
The two others would need to have the plates tied together. The paralleled plates of both would be the ground output of the rectifier bridge. The filaments would need to be connected to either end of the secondary.
As has been mentioned, much easier with indirectly heated tubes like 6AX4:
VinylSavor: Tube of the Month: The 6AX4
For higher voltages, exceeding about 900VDC a bridge with 6AX4 would also need separate heater windings. In the link above there is a schematic of such a bridge
Best regards
Thomas
Without seeing a three tube set-up for the 5U4GB....I dont understand...Duncans Sim program has the FWB using only two 5U4GB tubes??? Confusing?, yes!
Being that I have a bunch of 6AX4s., I can go that route...checking of course to srr if I have the slow, slower, slowest warm-up versions, four of them , matching.
____________________________________________________Rick..........
Being that I have a bunch of 6AX4s., I can go that route...checking of course to srr if I have the slow, slower, slowest warm-up versions, four of them , matching.
____________________________________________________Rick..........
Hi!
Duncans program does not list all possibilities how to do a FW bridge. You certainly cannot build a bridge with only 2 5U4. You need minimum three or better 4 so all legs use paralleled plates. You could also do a hybrid with one 5U4 and two 6AX4 for the ground legs. Or as has been mentioned one 5U4 with two SS diodes. Many possibilities
Thomas
Duncans program does not list all possibilities how to do a FW bridge. You certainly cannot build a bridge with only 2 5U4. You need minimum three or better 4 so all legs use paralleled plates. You could also do a hybrid with one 5U4 and two 6AX4 for the ground legs. Or as has been mentioned one 5U4 with two SS diodes. Many possibilities
Thomas
Richard,
What is the B+ rail voltage you are targeting? How much B+ current will the PSU have to provide?
A hybrid bridge employing 2X high PIV Schottky diodes, as the connection to ground, and 1 or 2 5U4's, depending on the amount of current needed, forming the "hot" legs rates to be your best bet. Both financial and technical reasons strongly favor the hybrid setup.
What is the B+ rail voltage you are targeting? How much B+ current will the PSU have to provide?
A hybrid bridge employing 2X high PIV Schottky diodes, as the connection to ground, and 1 or 2 5U4's, depending on the amount of current needed, forming the "hot" legs rates to be your best bet. Both financial and technical reasons strongly favor the hybrid setup.
This isn't difficult at all, and has been done lots.
You need just the one 5U4GB. You would use it to provide the positive rail, since that's how it was designed: two plates with a common cathode. That would make for one half of the bridge. The negative rail requires two singleton power diodes, preferably indirectly heated. This is required since there are no hollow state power diodes with separate cathodes and common plates.
It would look something like this (attached)
You would power up the heaters of the singleton diodes (TV damper diodes are used a lot for this purpose, and 6DE4s were used quite often as their specs are close to that of the 5U4GB) from a separate heater winding on the main PTX, or better still from their own heater PTX. As always, you need to pay attention to the Vhk ratings of the dampers, and also make sure that you're not exceeding their Isurge ratings in operation. The 6DE4 also had an advantage in that its forward drop is much lower than that of the 5U4GB.
This was done a lot in the making of ham rigs since the FWB configuration also makes for the so-called "economy" PS where the center tap provided a positive rail about half that of the main rail (for use powering RF final screens and/or low level stages).
Using DH types becomes more problematic in that each singleton will need its own PTX, thus the preference for IDH types. The whole thing requires two more holes in the chassis, more heater power, and costs a whole bunch of forward voltage drop. Hence, the preference for implementing these circuits with SS diodes.
Attachments
OK, Here's what I have for the amp, a PSE using 12B4s, single ended of course.
I have a decent collection of rectifyer tubes 5U4, 6AX4...
The mains transformer primary, 220VAC @50 Hz, The secondary I will be winding shortly and I will be running all my available wire on the bobbin. It is a pair of 10mH, eighteen gauge, 1.95 Ohm DCR coils....the wire size is slightly less than the primary. Once the first one is wound, I will splice in the second one & resume winding....this kind of precludes having a center-tap. Once all the wire is wound I will reassemble the TX & test for voltage. Once the maximum voltage is measured I will unwind turn by turn to get to my target voltage. I estimate I won't get much past 230 VAC.........aiming for 170 VDC.
The total current draw for the amp is an un-known (Don't know how to determine that).......The 5H coils is rated for only 100 mA....I doubt the total draw exceeds that value.
____________________________________________________Rick.........
I have a decent collection of rectifyer tubes 5U4, 6AX4...
The mains transformer primary, 220VAC @50 Hz, The secondary I will be winding shortly and I will be running all my available wire on the bobbin. It is a pair of 10mH, eighteen gauge, 1.95 Ohm DCR coils....the wire size is slightly less than the primary. Once the first one is wound, I will splice in the second one & resume winding....this kind of precludes having a center-tap. Once all the wire is wound I will reassemble the TX & test for voltage. Once the maximum voltage is measured I will unwind turn by turn to get to my target voltage. I estimate I won't get much past 230 VAC.........aiming for 170 VDC.
The total current draw for the amp is an un-known (Don't know how to determine that).......The 5H coils is rated for only 100 mA....I doubt the total draw exceeds that value.
____________________________________________________Rick.........
Attachments
Hi!
For this application 5U4s would be overkill. If you want to do a bridge with all tubes you can use 2 6BY5. They have two individual rectifier diodes in one bottle with their cathodes not connected. At these voltages you will also not get an issue with heater-carthode voltages, so both heaters can be run off one winding and referenced to ground.
See schematic here:
VinylSavor: The Modular Preamplifier, Part 4: Phono Stage PSUs
Best regards
Thomas
For this application 5U4s would be overkill. If you want to do a bridge with all tubes you can use 2 6BY5. They have two individual rectifier diodes in one bottle with their cathodes not connected. At these voltages you will also not get an issue with heater-carthode voltages, so both heaters can be run off one winding and referenced to ground.
See schematic here:
VinylSavor: The Modular Preamplifier, Part 4: Phono Stage PSUs
Best regards
Thomas
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